The transmittance properties of electrochromic materials change in response to electrically driven changes in oxidation state. Thus, when an applied voltage from an external power supply causes electrons to flow to (reduction) or from (oxidation) an electrochromic material, its transmittance properties change. In order to maintain charge neutrality, a charge balancing flow of ions in the electrochromic device is needed. By enabling the required electron and ion flows to occur, an electrochromic device utilizes reversible oxidation and reduction reactions to achieve optical switching.
Conventional electrochromic cells comprise at least one thin film of a persistent electrochromic material, i.e. a material which in response to the application of an electric field of given polarity, changes from a high-transmittance, non-absorbing state to a low-transmittance, absorbing or reflecting state. Since the degree of optical modulation is directly proportional to the current flow induced by the applied voltage, electrochromic devices demonstrate light transmission tunability between high-transmittance and low-transmittance states. In addition, these devices exhibit long-term retention of a chosen optical state, requiring no power consumption to maintain that optical state. Optical switching occurs when an electric field of reversed polarity is applied.
To facilitate the aforementioned ion and electron flows, an electrochromic film which is both an ionic and electronic conductor is in ion-conductive contact, preferably direct physical contact, with an ion-conducting material layer. The ion-conducting material may be inorganic or organic, solid, liquid or gel, and is preferably an organic polymer. The electrochromic film(s) and ion-conductive material are disposed between two electrodes, forming a laminated cell.
When the electrode adjacent to the electrochromic film is the cathode, application of an electric field causes darkening of the film. Reversing the polarity causes reversal of the electrochromic properties, and the film reverts to its high-transmittance state. Typically, an electrochromic film, such as tungsten oxide is deposited on a substrate coated with an electroconductive film such as tin oxide or indium tin oxide to form one electrode. The counter electrode is typically a similar tin oxide or indium tin oxide coated substrate.
As a voltage is applied across the electrodes, ions are conducted through the ion-conducting material. To ensure reliable operation, the ion-conducting material layer generally must be sealed so as to maintain its water content within a range sufficient to provide required ion conductivity. Also, to reduce optical distortion, the ion-conducting material layer should be of substantially uniform thickness.
The formation of a composite eyeglass lens by bonding front and rear lenses together is disclosed in U.S. Pat. No. 5,399,227. This bonding process in involves placing an adhesive on the concave surface of the front lens, pressing the convex surface of the rear lens against the adhesive on the front lens to spread the adhesive throughout the gap between the two lenses and permitting the adhesive to set to bond the lenses together.
U.S. Pat. No. 5,433,810 also discloses an eyeglass lens lamination method and apparatus which involves pressing lenses together to spread an adhesive between them. The adhesive is cured while the lenses are held together.
An apparatus for aligning and laminating the upper and lower lenses of a composite eyeglass lens is disclosed in Japanese Patent Application No. Hei 5[1993]-24872 and in Japanese Patent Application No. Hei 6[1994]-49600. The apparatus disclosed in these applications includes upper and lower lens retaining members. Each lens is held in its respective retaining member via vacuum and the retaining members are moveable. A bonding agent is applied to the center of the lower lens. The upper lens is then lowered until it touches the bonding agent on the lower lens after which aligning members move laterally to contact the peripheral edges of the upper and lower lenses to axially align them. A composite lens is removed after the bonding agent sets.
PCT/US97/07295 and copending U.S. application Ser. No. 08/970031 filed Nov. 13, 1997, now U.S. Pat. No. 5,916,398, disclose suspension lamination techniques for preparing laminated electrochromic devices
U.S. Pat. No. 5,471,338 discloses lamination of two coated plastic substrates using a layer of polymer which bonds with both coated surfaces to form a composite. Homo and copolymers of 2-acrylamido-2-methyl propyl sulfonic acid (AMPSA) form the ion-conducting polymer layer and are cured using actinic radiation, preferably (UV) light.
U.S. Pat. No. 5,327,281 discloses the use of a spacer to separate electrodes and contain a liquid electrolyte injected between the spaced electrodes.